In recent years, a system for processing information using a plurality of processors which operate in parallel has been popular. For example, a blade server is an information processing system which includes a plurality of blades. Each of the blades includes a CPU and a memory, and operates as a computer. The plurality of blades are accommodated in a chassis in the specified shape.
Each of the blades can transmit and receive data to/from other blades. Namely, the blades are connected through a transmission link. According to one embodiment, the blades are connected through a metal cable transmitting an electrical signal, such as a coaxial cable. In this case, a signal conforming to, e.g., a PCI (Peripheral Components Interconnect) is transmitted between the blades.
However, further increases in speed of information processing have been requested, and further increases in speed of a signal transmitted between blades have also been needed. For example, the transmission between blades of a high-speed signal with a speed exceeding 10 Gb/s is sometimes requested. For that reason, a configuration in which blades are connected through an optical interface, instead of the electric interface as described above, has been developed.
When an optical interconnection in which blades are connected through an optical interface is realized, each of the blades includes an optical module for transmitting and receiving an optical signal. The optical module includes an optical transmitting module and an optical receiving module. The optical transmitting module includes one or more electrical-to-optical converters (E/O converter) and corresponding drive circuits that respectively drive the E/O converters. The optical receiving module includes one or more optical-to-electrical converters (O/E converter) and corresponding amplifiers that respectively amplify outputs of the O/E converters. Therefore, when the density of the optical module increases, the power consumption of the optical module increases and an efficient heat radiation structure is needed.
As a related art, an optical waveguide board described below has been proposed. This optical waveguide board includes a base material, a film, an optical element, and an optical path switch. The film, in which an optical waveguide is formed that includes a core that is an optical path propagating an optical signal and a clad surrounding the core, is provided on a principal surface of the base material. The optical element is implemented on at least either of the base material and the film, and is optically coupled to the optical waveguide. The optical path switch changes the optical path propagating an optical signal in a desired direction. (For example, Japanese Laid-open Patent Publication No. 2004-258065)
As another related art, an optical module which includes an optical element which is flip-chip implemented on a board, an optical waveguide which is formed on the board and optically coupled to the optical element, and an underfill resin which is filled in between the board and the optical element and covers an optical connecting point between the optical element and the optical waveguide, has been proposed. (For example, U.S. Pat. No. 6,661,939)
As still another related art, an optical module which includes a flexible printed circuit on which optical elements (E/O and O/E) are flip-chip mounted, and an optical waveguide which is provided on the flexible printed circuit, has been proposed. A 45-degree mirror is formed in the optical waveguide so as to be optically coupled to a light emitting surface of the E/O and a photo detector surface of the O/E. (For example, Cost-effective On-board Optical Interconnection using Waveguide Sheet with Flexible Printed Circuit Optical Engine, Takashi Shiraishi, et al., OFC/NFOEC 2011, OTuQ5)
When the optical modules described in the related art document Shirasaki, etc., are mounted on a board (e.g., blade), an optical module may be attached to a blade so that a board of the optical module is disposed in parallel to the blade. In this case, an area occupied by the optical module is large in the blade.
In order to reduce the area for mounting the optical module, an optical module board on which a plurality of optical modules are mounted may be vertically attached to a mother board of the blade. However, in such a configuration, it is not easy to mount the plurality of optical modules on the optical module board with spatial efficiency and to efficiently dissipate heat generated in the optical modules.